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GCOS Ocean Sub-Surface ECV Definition: A measure of the quantity of dissolved salts in seawater. It is formally defined as the total amount of dissolved solids in seawater in parts per thousand (0/00) by weight when all the carbonate has been converted to oxide, the bromide and iodide to chloride, and all organic matter is completely oxidized. These qualifications result from the chemical difficulty in drying the salts in seawater. In practice, salinity is not determined directly but is computed from chlorinity, electrical conductivity, refractive index, or some other property with a relationship to salinity that is well established. The relationship between chlorinity Cl and salinity S as set forth in Knudsen's tables is S=0.03 + 1.805 CL. In 1940, however, a better expression for the relationship between total dissolved salts Σ and chlorinity was found to be Σ=0.07 + 1.811 CL. In more recent times, with the advent of devices that measure continuous records of conductivity electronically (e.g., CTD or conductivity–temperature–depth profiler), a new “practical salinity scale” has been determined. It is defined in terms of its electrical conductivity relative to a prescribed standard and it is given the units psu, for “practical salinity units.” For most purposes one can assume that the new unit, psu, and the older unit, 0/00, are synonymous. (From the AMS Glossary of Meteorology) A defining characteristic of ocean water is its relatively high concentration of dissolved salts or salinity. Understanding why the sea is salty begins with knowing how water cycles among its physical states: liquid, vapor, and ice. As a liquid, water dissolves rocks and sediments, and reacts with emissions from volcanoes and hydrothermal vents: this creates a complex solution of mineral salts in our ocean basins. In other parts of the cycle, however, water and salt are incompatible: water vapor and ice are essentially salt free. More...(from the NASA Goddard Space Flight Center web site) Introduction: Systematic sampling of the global ocean is needed to fully characterise oceanic climate variability. Global implementation of upper-ocean measurements in ice-free regions is technically feasible, with proven techniques, but remains to be accomplished. This will be addressed initially through the implementation of the agreed upper-ocean network, the in situ component of which initially requires 3000 Argo profiling floats, about 40 repeat XBT lines, 30-40 surface reference moorings, and about 120 tropical moorings, together with high-precision satellite altimetry. Similar to the surface, the Global Reference Mooring Network will provide essential reference-quality long-time records of sub-surface variables to identify climate trends and climate change. They also provide critical platforms for the testing and pilot project use of technology for autonomous measurement of biogeochemical and other ecosystem variables. The records from the Global Reference Mooring Network also will be important for testing climate models and their parameterizations. As new technologies are proven, as our understanding of the sampling requirements improves, and as our ocean analysis and reanalysis capabilities are exploited, the recommended global sub-surface observing system will evolve. WCRP will encourage the development of ocean climate reanalyses, including all appropriate historical data assimilated into ocean models, to create climate variability and trend analyses, and to support seasonal-interannual to decadal climate prediction. They will also encourage other efforts to develop analyses and reliable datasets and products of climate variability and trends.
Sub-surface Salinity: Knowledge of the sub-surface salinity variability and change is essential in improving seasonal and interannual prediction and understanding the impact of changes in the hydrological cycle on ocean circulation. It can be observed with existing technology, but this ECV is not adequately sampled globally at present. The agreed programme will dramatically increase our knowledge of this ECV. Repeating XCTD observations from ships of opportunity are also feasible. Additional Information:
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Data, Product, Metadata and Information Access [ECV Matrix Main Page] [About the ECV Matrix] [Reference Documents] [Contact] [Updated February 25, 2011]
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